1. Field of the Invention
The present invention relates to a rotary head cylinder for a magnetic recording and/or playing-back device, such as a video tape recorder, and more particularly to a rotary head cylinder which guides the magnetic-tape running round a portion of the cylinder's outer periphery and which is, with a magnetic head, suited for recording and/or reproducing signals such as video signals on magnetic tapes, and the method for manufacturing such rotary head cylinders.
2. Description of the Related Art
Recently, rotary head cylinders (hereinafter, referred to as "cylinders") have been worked on to reduce the weight, along with the trend of a smaller and lighter body of a magnetic recording and/or playing-back device. An idea has been proposed that the outer ring of a cylinder for touching a tape be molded of a material with high resistance against wear-and-abrasion and corrosion, such as high tensile aluminum alloy, and that the inner portion be molded of a material, such as aluminum alloy for die casting or synthetic resins.
A known method for manufacturing cylinders will be explained, hereinafter, with reference to FIGS. 1, 2. FIG. 1 shows a known method for manufacturing cylinders. FIG. 2 is a sectional view of a cylinder manufactured in the known method as shown in FIG. 1. A fixed metal mold 1 has a cavity. A movable metal mold 2 has a projection and moves to close the cavity of the fixed metal mold 1. An outer ring 3 providing a surface contacting with tapes and made of high tensile aluminum alloy is beforehand shaped in desired dimensions (outside diameter, thickness, and width). Reference numeral 4 refers to filling holes through which a material such as die-casting aluminum or a synthetic resin fills the cavity of the fixed metal mold 1.
A cylinder is manufactured in the above manufacturing device as follows. The outer ring 3 of the cylinder, made beforehand of high tensile aluminum alloy in a desired shape, is put in the cavity of the fixed metal mold 1, and the projected movable die 2 moves to close the cavity. Thus the molding cavity is formed.
Next, a material such as die-casting aluminum alloy or a synthetic resin is injected through filling holes 4. Then, after cooled, a cylinder with its outer ring 3 and inner ring 5 integrally coupled, as shown in FIG. 2, is taken out.
Finally, the outer periphery of the cylinder is ground, and grooves and head windows are defined by machine cutting or such, to be finished into a rotary head cylinder.
In the conventional method, the outer ring 3 and the inner ring 5 do not couple strongly enough, so that the outer and inner rings may slide on each other and, in some case, come apart. Therefore, the inner surface of the outer ring 5 has to be rugged, e.g. under the knurling process, to reinforce the coupling of the outer and inner rings 3, 5. However, such a special process still fails to enhance the coupling rigidity up to a satisfactory level and requires more work, lowering the work-efficiency.